warehouse slab suggestions

[a2mfk]

Have a client who is unable to provide us any meaningful information about their light industrial and warehouse slab. They just are useless in this department.

Racks similar to "home depot" and could be that tall (b.o. steel around 26ft), storing rather lightweight boxes of vitamins, supplements, etc. Forklifts similar to home depot, we don't know about the traffic (I'd guess light to medium). We know no other details and at this time in regards to weights, rack post spacing, base plates, etc.

Conditioned space in Florida. Sawcut control joints probably around 10' o.c., not sure about WWF, rebar or steel fibers yet.

I was thinking of giving them a design for a couple of different slab sizes and reinforcing schemes, and give them my basis of design, and then they can choose. Maybe in table form on the foundation plan.

I welcome any opinions, especially on conservative rack point loads and base plate sizes, spacing of rack posts, and slab thickness. I have been told by those in the know that the "Cadillac" of warehouse slabs would be #3 @ 14-18" o.c. E.W.

Semi rigid epoxy to fill the CJs, any favorites?

And probably most importantly, I was not planning on providing dowels at CJs , maybe only at construction joints (pour stops for the day...)

I have Part 2 of the ACI Manual of Practice.

Thanks in advance.

 

[a2mfk]

I just realized I need 360R, and that is not included in Part 2... I will look to borrow it.

 

[hawkaz]

Watch out for forklift loads (especially hard wheel)- these can impact this type of slab (especially the joints) as much or more than racks.

Don't know much about the soils in FL. Slab thickness will vary based on your subgrade modulus. Based on the limited info so far, this could be 6" to 8" thick.

You are asking for trouble if you don't do something at the joints. I would call out diamond dowels and dowel backets at all joints.

Reinforcing really doesn't do too much as long as the joints are spaced properly and the diamond dowels/dowel baskets are installed. Don't waste the owners money on fibers.

 

[a2mfk]

Clean sand, we usually get 2500-3000psf for our foundations with basic compaction... Moisture barrier, no gravel, just a sand sub-base.

k=150pci

I am going to borrow or download ACI360R, I have been told this has pretty much all I need. I know how to run the numbers, though its been a long time.

Any do's and don'ts or recent success stories, etc.?

 

[HeavyCivil]

There is a Text by Ringo and Anderson that goes through design examples by multiple authorities (PCA for example) that does a good job of sizing your slab based on loading (wheeled vehicles, racks etc) and subgrade. I would consider that to be more valuable that ACI360 for actual design. ACI360 is a good source for detailing and good practices but if I remember correctly it won't help you arrive at a thickness based on loading and subgrade.

You may be able to find the PCA charts online as well and avoid purchasing the book.

 

[msquared48]

State your design assumptions and constraints within a written contract, stating that any changes will be considered extra services, get them to sign it, and run with it. It may turn out to be a wet sponge filled with milk for you! Not a bad circumstance for you in this economy.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ToadJones]

I like Sika's products.

 

[a2mfk]

Toad- do you have a specific product for control joints subject to forklifts that you like?

 

[ToadJones]

I want to say Sikadur 5l SL or something like that.
Sika has about ten trillion products.
Check out their website.

I have been simply amazed by the long term flexibility & strength of their joint/crack products.

 

[OHIOMatt]

I would not do this type of slab without a crushed stone base of 6" minimum. Sand will rut far too easily under the load of concrete truck and laser screeds.

As hawkaz stated, take care of all joints. You will have curling no matter how careful. A curled edge will crack, joint reinforcing helps.

I have had success with Metzger/McQuire MM80. You should note that joint filler will separate due to concrete shrinkage. Place in the specs that the GC will need to come back and repair.

Rack loads as you describe will likely not have much impact on the deisgn. Fork lifts, even lightly loaded will.

 

[ToadJones]

OHIO-
Is it necessary to fill the joints so soon that shrinkage is a big problem?

 

[hokie66]

In establishing design criteria, I wouldn't make the assumptions too light. Rack loading can change, especially if the warehouse is a rental proposition. Assuming the lightest loading might save a few dollars in the initial construction, but could make the warehouse unusable for a different business.

Shear transfer at the joints is a must. Agree with hawkaz that diamond dowels are a good solution, as are the square dowels with compressible material on the sides (known as Danley dowels here in Australia).

May be too much too soon for your project, but I believe "jointless" floors with steel fibres will be the standard in the future. Rather than slab thickness, reinforcement, concrete strength, even what the slab is sitting on, the joints are most often the problem...and that is regardless of the spacing of the joints.

 

[a2mfk]

If I ever want to get another job in Florida I will not be specifying 6" of crushed rock. Maybe that is a superior subgrade, but its not done here ever, that I know of... Only as a sub-base for asphalt. The natural sand here if it is well graded, and the type used in fill compacts quite nicely and you can drive over it no problem (remember the original Nascar races were done on the beach in Daytona, and you can drive on lots of beaches, for example). I imagine this will all be pumped with a boom anyway.

Agree that poly fibers are a waste, though I know some engineers that work with steel fibers in this type of application and have success. I am currently planning on WWR or rebar for shrinkage, thickness sized for forklifts per PCA or Army Corps method, and also doing some rack load checks using other methods I have found. Right now I am thinking a 6" slab will meet all of our assumed criteria.

Is it normal to give a minimum offset of racks from CJs? I guess if you use dowels this doesn't matter quite so much...

So with forklifts, doweled joints or similar are a must, huh? Even light forks carrying a pallet of boxes of vitamins, WWR or rebar cont. through the joints won't suffice?

Also in regards to shrinkage, what about placing these in staggered strips, and then infilling a couple of days? This allows free movement in the short direction, and then you have CJs in the long direction.

Good point on the filler, my research has indicated the best method is to have the joints filled as late in the construction process as possible. Hopefully at least a couple of months or more will have passed while they build out the office and do exterior finishes. This will minimize the amount of opening of the joints.

Thanks for all of your input.

 

[a2mfk]

What about PCA's book on Concrete Slabs on Ground? If I were to buy one design guide on the subject, would this be the one?

 

[dik]

SLAB SAWCUT AND CONTROL JOINT SEALANTS TO BE:
SIKA LOADFLEX 2 IN HEAVY TRAFFIC AREAS
SIKA DUOFLEX SL IN MODERATE TRAFFIC AREAS
SIKA DUOFLEX SL IN LIGHT TRAFFIC AREAS

Critical that sawcutting be done at the right time. Joints can be 1/4" wide to get sealant in place, and for a 6" slab, 1-1/2" deep and for an 8" slab, 2" deep. I place rfg at 1-1/2" clear cover for 6" and 2" clear cover for 8".

Rack loading, depending on the loads can be critical for elastic tensile stresses. Point loading can increase or decrease flexural tensile stresses, depending on the spacing, concrete strength and soil modulus. I use an old (30 years approx) PCA airport pavement program to calculate concrete flexural stresses.

I use 6mil PEVB under slabs (some people swear by them some at them) and 6" well compacted 'A' base to 95% MPDD. Curing the slab is critical, also.

Dik

 

[a2mfk]

Dik- we always use 10mil, been told 6mil tears easily and have read some articles about vapor transmission through 6mil can lead to flooring problems. We have a high water table in many areas of FL and moisture intrusion through slabs in flooring problems are common.

Thanks for the other suggestions.

I just found what appears to be a very well done and well-documented Excel program on this very subject, I downloaded it and no viruses and it looks good. Have not had time to play with it yet, gotta go hang with the wife before bed here or I am in trouble.

Google- "GRDSLAB" Program

 

[a2mfk]

Dik- whats "A" base? DOT Terminology maybe...?

 

[dik]

A Base or Granular A is a well graded crush that compacts well.

GRANULAR 'A' (GRAVEL)
CRUSHED ROCK COMPOSED OF HARD DURABLE UNCOATED FRACTURED FRAGMENTS PRODUCED FROM ROCK FORMATIONS OR BOULDERS OF UNIFORM QUALITY, OR A MIXTURE OF CRUSHED GRAVEL, SAND AND FINES COMPOSED FROM NATURALLY FORMED DEPOSITS ONFORMING TO THE PROVINCE OF MANITOBA SPECIFICATIONS FOR AGGREGATE FOR GRANULAR BASE COURSE FOR CLASS A

FILL SHALL CONFORM TO:
SIEVE SIZE (ASTM) PERCENT PASSING
3/4 INCH 100
5/8 INCH 80-100
NO 4 40-70
NO 10 25-55
NO 40 15-30
NO 200 8-15

Dik

 

[dik]

Thanks for the info on using 10 mil...

Dik

 

[Ron]

A2...you have the right ideas, you're just looking for us to share in your misery!!

With forklift traffic, I would dowel the joints. Others have suggested plate dowels. They're not common in our area but they work reasonably well for light loads. Otherwise, use standard pavement dowels, as long as the slab thickness is at least 6".

I like Sika products as well, but have also had good success with W.R. Meadows Rezi-Weld Flex, a semi-rigid epoxy joint filler.

As for the racks, design for the maximum capacity of the rack, not the stated inventory. Require that rack capacities be posted on the racks and on the walls.

You won't be able to avoid racks bearing near control joints. Obviously, see if you can get a rack layout before designing the slab. Punching controls. k=150pci is fine...you could go to 200, but it won't make much of a change in the thickness.

Slab on 10-mil vapor barrier over compacted sand is fine. Done all the time. Put some controls on the "flatness" tolerance of the subgrade as well as the slab...that will help meet thickness tolerance requirements and cut down on "random" cracking. Steel fiber in lieu of WWF is a very good change. I have experience with steel fiber in slabs, exterior and interior...good results. Have one that I designed for an approach apron for loading dock and dumpster area in 1987....still performing great.

Make sure the mix design uses the largest coarse aggregate practicable for the application. The contractor will want to pump the slab, but if so, make sure that you stick to a large aggregate to cut down shrinkage and assist in load transfer (although that doesn't really work very well). This is not the type of job to use a 2" Mayco pump behind a pickup truck.

Stick to your guns on the timing, depth, and spacing of control joints. Important.

Require a flatness tolerance...Ff of 30 or more.

Good luck.